Exhaust-gas treatment devices in which a liquid additive is required for exhaust-gas purification purposes are known in the automotive sector for example for reducing nitrogen oxide compounds in the exhaust gas of an internal combustion engine. In exhaust-gas treatment devices of this type, the method of selective catalytic reduction (SCR) is normally implemented. In this method, nitrogen oxide compounds in the exhaust gas of the internal combustion engine are reduced with the aid of ammonia. Ammonia is normally stored in motor vehicles not directly but rather in the form of a liquid exhaust-gas additive which is converted outside the exhaust gas or within the exhaust gas to form ammonia. A urea-water solution is particularly commonly used as a liquid exhaust-gas additive for this purpose. A 32.5% urea-water solution which is available under the trade name AdBlue® is particularly widely used.
A delivery unit is normally used for delivering liquid additive of this type to the exhaust-gas treatment device. A problem of such a delivery unit is that the liquid additive for the exhaust-gas purification can freeze at low temperatures. The urea-water solution described above, for example, freezes at −11° Celsius. In motor vehicles, such low temperatures may arise for example during long standstill phases in winter. When freezing occurs, the liquid additive undergoes a volume expansion, which may damage a delivery unit for delivering the liquid additive. Accordingly, it is necessary and advantageous for a delivery unit for delivering liquid additive to be constructed so as not to be destroyed by volume expansions that occur in the event of freezing.
It is known for compensation elements to be provided for compensating the ice pressure in a delivery unit. Such compensation elements are however additional components which make the structural design of a delivery unit for liquid additive more complicated.